(1) Field of the Invention
The present invention relates to ejectors and more closely to what is called multi-ejectors in which several ejector nozzles are located successively and in some embodiments also beside each other.
(2) Description of the Prior Art
By the aid of such ejectors it has been possible when using a positive pressure of about 4 kiloponds per square centimeters to reach negative pressures corresponding to about 50% of the actual air pressure. However, it has been a desideratum to reach lower negative pressure in connection with corresponding relations.
Said desideratum has, indeed, to some extent been reached by an arrangement of ejector nozzles in the way described in Swedish patent application Ser. No. 7905309-6 and in connection therewith a negative pressure corresponding to about 7% of the actual air pressure has been obtained. However, for many fields of use also this good value is unsatisfactory, such as in connection with the manufacturing of bulbs, freeze-drying of food and similar.
In connection with manufacturing processes using negative pressures there are problems which not always are realized. To conduct negative pressures request generally more large-sized conduits than to conduct positive pressures. Conventional vacuum pumps are rather bulky and cannot be located in direct connection with the chamber or the object within which the negative pressure is desired. The result is that large-sized conduits are to be extended between pump and chamber or object.
Ejectors of the type of which the present invention refers are small light units which may be placed in direct connection with the place of use. Due to the fact that they are driven by positive pressure, i.e. compressed air, they need only narrow supply conduits therefor, simultaneously as the risks of problems due to electrical faults do not exist, something that might be present in connection with the conventional vacuum pumps. Further, the ejectors are of a simple and reliable structure, a fact that gives rise to an extra ordinary reliability in operation. Further, in comparison with conventional vacuum pumps multi-ejectors show the advantage that their capacity is very great at the same effect consumption. This means that the first part of an evacuation takes place very fast, of course depending on the fact that they do not work with any conventional stroke volume. The greater volume to be evacuated the greater economical importance this effect has as the time of evacuation is essentially shorter than with the use of conventional vacuum pumps.